Abstract
Factors causing the cyclic changes in the rates of net photosynthesis and transpiration of peanut plants were examined. In order to clarify the relationship between the transpiration demand and the occurrence of the cyclic changes, relative humidity (R.H.) of the air introduced into the assimilation chamber was altered. When R.H. (at 25°C) of the air at the entrance of the assimilation chamber was 25±5%, about 90% of the plants showed the cyclic changes in the net photosynthetic rate and the transpiration rate. However, only a few plants showed the cyclic changes when R.H. of the air was 65±5%. This implies that large transpiration demand due to low air humidity induced the cyclic changes in the rates of net photosynthesis and transpiration. When the transpiration of a part of the leaves was suppressed by covering with aluminum foil, the cyclic changes in the rates of net photosynthesis and transpiration were disappeared. Partial excision of the root system of the plants which did not show the cyclic changes even in the low humidity air, induced the cyclic changes. These results suggest that both the large transpiration demand and the low capacity of water supply are important factors in the occurrence of cyclic changes in the rates of net photosynthesis and the transpiration of peanut plants. Possibly, individual differences in the appearance of the cyclic changes under low air humidity were associated with the water uptake ability of individuals.
